Phocess for treating nylon



March 1964 F. 1.. LARKIN ETAL PROCESS FOR TREATING NYLON FILAMENTS I TO ATTORNEY Filed April 10, 1961 MICHAEL/fl FRANK LL BY r 4m 7m. Mar

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United States Patent Delaware Filed Apr. 10, 1M1, Ser. No. 102,052 4 Claims. (Cl. 264-290) This invention relates to the treatment of nylon filaments. More particularly, the invention relates to a process of treating nylon filaments so that they have a reduced tendency to retract.

Nylon filaments normally are produced by a manufacturer at one location and are shipped in package form to customers at distant locations. The customers convert the filaments into fabric or other products.

Conventionally, the filaments are wound on a yarn holder such as a bobbin, pirn, cone or the like before they are shipped. The yarn holder ordinarily is constructed of rather rigid and expensive material. Accordingly, economics dictate that the holder be a returnable item. That is, the customers must return the yarn holder to the filament manufacturer after the filaments are removed therefrom. While it would be desirable to ship the filaments on a disposable yarn holder such as one made of paper, nylon yam has a drawback of developing a tendency to retract in length after a period of time on the holder, thus giving rise to considerable compressive forces that would crush paper yarn holders of the conventional type. It has been known for some time that the tendency of nylon filaments to retract can be reduced by heating the filaments while under little or no tension. Unfortunately, the reduced retraction of the filaments is gained at the expense of obtaining filaments which have a low initial modulus. Recently, a method has been disclosed whereby nylon filaments are treated under certain conditions such that the reduced retraction tendency is ac complished without considerable lowering of initial modulus. Such method does not permit treatment at the high speeds commercially desired today.

It is, therefore, an object of the present invention to provide a commercially acceptable process for producing nylon filaments having a reduced tendency to retract in length. A further object is to provide a process for drawing nylon filaments at a rapid and efiicient rate, the drawn filaments having a reduced tendency to retract, high initial modulus and other excellent characteristics.

Other objects will be apparent from the following detailed description.

Generally, the objects of this invention are achieved by stretching nylon filaments in two different stages under controlled conditions and thereafter heating the filaments while the filaments are under low tension permitting the filaments to relax. Following the relaxing operation, the filaments are taken up in an orderly manner. The resulting filaments can be stored on conventional paper yarn holders. Due to the reduced tendency of the filaments to retract on standing, inexpensive paper holders may be used without fear of their collapsing. The reduced retraction is obtained without significant sacrifice in the initial modulus of the filaments or production speed thereof.

Nylon filaments capable of being molecularly oriented, such as freshly spun filaments or as spun filaments, are fed longitudinally to a first stretch zone at a predetermined rate and are withdrawn therefrom at a predetermined increased rate so that the filaments are attenuated to increase the molecular orientation thereof. The draw ratio employed in the first zone is determined by the overall draw ratio and the draw ratio employed in the second 3,124,632 Patented Mar. 10, 1964 'ice stretch zone. The overall draw ratio, i.e., the number obtained by dividing the speed of the yarn fed to the first Zone into the speed of the yarn leaving the second zone, can be about as low as 2.5 and about as high as 5.5, depending on the orientation of the spun filaments and the orientation desired in the filaments after processing. The optimum draw ratio for each bundle of filaments can be determined empirically. In the first zone the filaments are snubbed so that there is a tendency of the point of necking down of the filaments to be localized. This may be accomplished by the use of a snubbing pin, roll, or the like. When snubbed, the yarn temperature in the first zone can be about 20-85 C. The partially oriented filaments are passed upon their exit from the said first zone to a second stretch zone and there heated to a temperature of about C. to 220 C. The heat is applied while the filaments are being stretched a controlled amount and thus while the filaments are under considerable tension. After attaining the desired temperature, the filaments are subjected to a draw ratio of about 1.2 to 1.9 in the second stretch zone. As will be appreciated, the draw ratio of the first zone times the draw ratio of the second zone will equal the overall draw ratio. The filaments should be snubbed during the second drawing and are stretched to a highly oriented state. Then the filaments are heated under low tension so that they are relaxed while being heated, the same temperature as employed in the second zone being entirely suitable. The relaxed, heated filaments are permitted to shrink a controlled amount of about 610 percent. Thereafter, the filaments are taken up in an orderly manner by conventional means.

One form of apparatus for treating the filaments in the multi-stage operation herein described includes suitable means for supplying molecularly orientable filaments from a source at a predetermined rate. A first yarn forwarding means is provided in the yarn path and is adapted to forward the yarn at a speed such that the filaments are stretched a predetermind extent between the supplying means and the forwarding means. Disposed in the yarn path therebetween is a yarn snubber to apply a predetermined resistance to the forward movement of the yarn so that the point of stretching of the filaments is localized. A second yarn forwarding means is provided in the yarn path and is adapted to be operated at a predetermined increased rate as compared with the rate of the first yarn forwarding means so that the yarn is stretched an additional amount. In the yarn path between the first and second yarn forwarding means a second yarn snubber is positioned. This second snubber is provided with means so that its yarn engaging surface is maintained at an elevated temperature. Means for taking up the yarn in an orderly manner is provided without subjecting the yarn to high tensioning. In the yarn path between the take-up means and the second forwarding means, a heating element is positioned so that the yam is heated. Since the yarn is under low tension at this point, the yarn will be heat-relaxed.

In a second form and the preferred form of the apparatus, one of the yarn forwarding means can be omitted to provide obvious economic and mechanical advantages in that less moving parts are needed and less space for the apparatus is required. In this second arrangement two snubbing pins, or the like, are disposed in the yarn path between the means for supplying the filaments and the yarn forwarding means. The filaments will be snubbed in tandem by the pins; and thus, the filaments are stretched in two stages without an intermediate yarn forwarding means.

The amount one draws the filaments in the first stretch zone is important since the filaments before being subjected to the subsequent steps should exhibit some increased degree of molecular orientation as compared with the orientation of the filaments as spun. Increasing the molecular orientation of the filaments in the primary stretching stage, when carried to extremes, hinders the filaments from accepting the benefits in regard to reduced retraction and yarn quality bestowed to them by the subsequent steps of the method. If the orientation of the filaments is not sufficient, the same hindrance is present. As indicated above, the amount of draw in the zone ordinarily is computed once the overall draw ratio and the draw ratio in the second stretch zone have been selected. It is important that the filaments during their travel through the first stretch zone be snubbed so that there is a tendency of the point of draw to be localized. The ambient temperature in the first zone can be that ordinarily employed in the conventional single stage cold drawing of nylon filaments. At the point where the yarn is snubbed the temperature can be about 2085 C., although the preferred temperature range is 3580 C.

After being stretched in the first zone, the filaments are continuously heated an simultaneously given a secondary stretch. As indicated above, the temperature at which the second stretch is carried out can be in the range of 130 C. to 220 C., although the most satisfactory range is 160 C. to 200 C. One preferred embodiment of the invention comprises heating the partially oriented filaments with dry heat, such as by passing them over a heated surface in contacting engagement therewith. The filaments while heated are stretched and are under considerable tension. In the secondary stretching step, the filaments are subjected to a draw ratio of about 1.2-1.9, preferably about 1.4-1.7. I When stretching is completed, the filaments are heatrelaxed. The post heat-relaxation is quite important to the practice of the invention. In a preferred embodiment heating is accomplished by passing the filaments over the heated snubbing pin while the tension of the filaments is sufficiently low to permit the yarn to shrink about 6-10 percent. The filaments are thereafter taken up in an orderly manner.

The invention is further illustrated by reference to the drawing wherein:

FIGURE 1 is a schematic view in perspective with principal parts in location illustrating one arrangement of apparatus suitable for treating nylon filaments in accordance with the present invention; and

FIGURE 2 is a schematic view illustrating a second embodiment in which one yarn forwarding means is Omitted.

Yam 1 to be treated and composed of a bundle of smooth substantially parallel filaments that have not been fully oriented is supplied from a yarn source 2. The yarn source can be, for example, a package previously doifed from a conventional spinning machine, as illustrated. However, the apparatus can readily be adapted for processing continuous yarn which is supplied directly from the spinning machine without an intermediate take up. Yarn 1 is passed over and around one end of a bobbin or other yarn holder. The yarn is threaded through a guide 3 and around a snubbing bar 4 which functions as a simple, uncomplex tensioning device to assist in maintaining an orderly and uniform supply of yarn. From the tensioning device the yarn is passed through a guide 5, if needed, and then to a rotatably arranged thread advancing means comprising a pair of feed rolls 6 and '7, at least one of which is positively driven. The rolls engage each other to nip the yarn. The yarn is led around a first snubbing pin 8 or like snubbing means. The pin preferably is mounted to be non-rotative and has a smooth yarn contact surface made of resistant-to-wear material.

After being passed around pin 8 a desired number of times, yarn 1 is directed around a rotatably mounted draw roll 9 and its associated separator roll 10 which is freely rotatably mounted. Roll 9 is positively driven at a pcs ripheral speed such that the yarn is given a predetermined stretch between roll 7 and roll 9 which define the first stretch zone A. Next, the yarn is led around a second snubbing pin 11 or the like and thence around a driven roll 12 and its associated separator roll 13. Roll 12 is driven at a peripheral speed such that the yarn is given a predetermined stretch between roll 9 and roll 12. The second pin 11 is heated to provide a source of dry heat for raising the temperature of the yarn while it is being snubbed. The heating of the pin can be achieved in a suitable manner, e.g., by internal electric resistant heating.

After being stretched sufliciently in the two stages, the tension on the yarn is reduced. While under reduced tension, the yarn is heated. This can be accomplished by passing the yarn across the surface of a heated pin 14 or the like. By properly locating the parts, the yarn while under low tension can be passed a second time around pin 11, thereby eliminating the need of pin 14.

The yarn after being heat-relaxed is taken up in a conventional manner by a suitable form of a package building apparatus such as a ring twisting assembly or the like. The yarn passes through a guide 15 and is wound on a package 16 by means of a vertically-reciprocated ring 17 carrying a traveller 18 adapted to revolve freely around the package.

In the embodiment of FIGURE 2 draw roll 9 and separator roll 10 are omitted. Hence, the string up involves passing the yarn around pin 8 a desired number of times and then around heated pin 11. Pins 8 and 11 will snub the yarn to provide the snubbing in the primary stretch zone A and in the secondary stretch zone B, respectively.

The following examples will serve to illustrate the invention, although they are not intended to be limitative. The yarn employed in each case was melt spun from nylon-66 (polyhexamethyleneadipimide). However, yarn prepared from other types of nylon polymer can be processed in accordance with the present invention. Other types of nylons include nylon-4, nylon-6, nylon-610, nylon-11, and their fiber-forming copolymers, e.g., 6/66, 6/ 610/ 66, 66/610, etc. Nylon, as is well-known, has recurring intralinear carbonamide groups as an integral part of the main molecular chain.

EXAMPLE I In accordance with a conventional cold-drawing procedure, a 17 filament nylon-66 yarn with a spun denier of 138 was advanced by means of a pair of feed rolls to a stretch zone. The yarn was wrapped two times around a snubbing pin and then around a draw roll and a separator roll. The yarn was wound onto a bobbin by means of a ring twister take-up device. The balloon tension was 6 to 8 grams. The draw ratio was 2.91, and the peripheral speed of the draw roll was 588 yards per minute. During the processing of the yarn the snubbing pin had a temperature of 55 C. maintained by the friction of the yarn pulled therearound. The physical properties of the resulting yarn are given below in the table.

EXAMPLE II In this example the apparatus of FIGURE 2 was employed except that pin 14 was not used so that the yarn was not given a post heat-relaxation treatment. A 17 filament nylon-66 yarn with a spun denier of 138 was advanced by means of a pair of feed rolls 6 and 7 to a two-stage stretch zone. The yarn was wrapped around pin 3 which had a temperature of 55 C. Next, the yarn was passed around draw pin 11. The speed of the yarn supplied to pin 11 with respect to the speed of the yarn delivered by rolls 6 and 7 was such that the draw ratio in the first draw stage was 2.50. The yarn was pulled from pin 11 by means of draw roll 12 and separator roll 13 at a speed such that the yarn was stretched a second time. The speed of the yarn leaving the draw roll was 588 yards a minute. The overall draw ratio of In this example the apparatus of FIGURE 2 was employed. A 17 filament nylon-66 yarn with a spun denier of 138 was advanced by means of a pair of feed rolls 6 and 7 to a two-stage stretch zone. The yarn was wrapped around pin 8 which had a temperature of 55 C. Next, the yarn was passed around draw pin 11 maintained at 185 C. The speed of the yarn supplied to pin 11 with respect to the speed of the yarn delivered by rolls 6 and 7 was such that the draw ratio in the first draw zone was 2.50. The yarn was pulled from pin 11 by means of draw roll 12 and its separator roll at a speed such that the yarn was stretched a second time. The speed of the yarn leaving the draw roll was 588 yards per minute. The overall draw ratio of the process was 2.91. The yarn was then passed around pin 14 maintained at 185 C. under a tension of less than grams so that the yarn was heat-relaxed. The yarn was wound onto a bobbin by means of a ring twister take-up device; the balloon tension during the take up was 6-8 grams. The physical properties of the resulting yarn are given below in the table, from which it is seen that the yarn processed in accordance with the present invention has substantially reduced retraction and shrinkage without sacrifice of other properties.

EXAMPLE IV In accordance with a conventional cold-drawing procedure, a 17 filament nylon-66 yarn with a spun denier of 138 was advanced by means of a pair of feed rolls to a stretch zone. The yarn was wrapped around a snubbing pin maintained at 55 C. and then around a draw roll and a separator roll. The speed of the yarn leaving the draw roll was 568 yards per minute. The yarn was Wound onto a bobbin to form a cylindrical package of zero-twist yarn utilizing conventional traverse means and means to rotate the bobbin. The yarn was wound onto the bobbin at a tension of 5-10 grams. An underdrive of 8% was used; that is, the yarn wind-up speed was 0.92 of the peripheral speed of the draw roll. The draw ratio was 2.91. The physical properties of the resulting yarn are given below in the table.

EXAMPLE V In this example the apparatus of FIGURE 2 was employed except that pin 14 was by-passed and the yarn Was wound up without being twisted. A 17 filament nylon-66 yarn with a spun denier of 138 was advanced by means of feed rolls 6 and 7 to a two-stage stretch zone. The yarn was wrapped around pin 8 which had a temperature of 55 C. Next, the yarn was passed around draw pin 11. The speed of the yarn supplied to pin 11 with respect to the speed of the yarn delivered by rolls 6 and 7 was such that the draw ratio in the first draw stage was 2.50. The yarn was pulled from pin 11 by means of a draw roll 12 and a separator roll at a speed such that the yarn was stretched a second time. The speed of the yarn leaving the draw roll was 568 yards per minute. The overall draw ratio of the process was 2.91. The temperature of pin 11 was maintained at 185 C. The yarn was then wound onto a bobbin to form a cylindrical package of zero-twist yarn utilizing conventional traverse means and means to rotate the bobbin. The yarn was Wound onto the bobbin at a tension of 5-10 grams. An underdrive of 8% was used. The physical properties of the resulting yarn are given below in the table.

EXAMPLE VI In this example the apparatus of FIGURE 2 was employed except that the yarn was wound up in a cylindrical form without being twisted. A 17 filament nylon-66 yarn with a spun denier of 138 was advanced by means of feed rolls 6 and 7 to a two-stage stretch zone. The yarn was wrapped around pin 8 which had a temperature of 55 C. Next, the yarn was passed around draw pin 11. The speed of the yarn supplied to pin 11 with respect to the speed of the yarn delivered by rolls 6 and 7 was such that the draw ratio in the first draw stage was 2.50. The yarn was pulled from pin 11 by means of a draw roll and a separator roll at a speed such that the yarn was stretched a second time. The speed of the yarn leaving the draw roll was 568 yards per minute. The overall draw ratio was 2.91. The temperature of pin 11 was C. The yarn was then passed around pin 14 maintained at 185 C. under a tension of less than 25 grams so that the yarn was heat-relaxed. The yarn was wound under a tension of 5-10 grams with an underdrive of 8% being used. The physical properties of the resulting yarn are given below in the table, from which it is seen that the yarn processed in accordance with the present invention has substantially reduced retraction and shrinkage without sacrifice of other properties.

Table Initial Retrae Shriulr- Elongar Tenacity Ex. N0. Modulus, tion, age, tion, percent g.p.d. percent percent percent Percent yarn retraction may be defined as quotient of the reduction in length of yarn of a given length occurring in 24 hours while under substantially no tension and the given length times one hundred. A procedure for measuring this includes reeling 225 meters of yarn from a bobbin to form a skein of yarn. The skein is suspended for 24 hours at a temperature of 23 C. and at a relative humidity of 68%. The length of the yarn after the 24 hours is measured and the percent retraction computed.

For determining the residual yarn shrinkage, the skein of yarn after the percent retraction is determined is boiled in water for 60 minutes and then hung up to dry for 24 hours. The length of the dried skein of yarn is measured. The shrinkage is the quotient of initial length of yarn minus the length thereof after boiling, divided by the initial length of yarn times one hundred.

The initial modulus is defined as the ratio of change in stress to strain in the first linear portion of a stressstrain curve. The ratio is calculated from the stress, ex pressed in force per unit linear density, and the strain expressed as percent elongation. As the strain is ex pressed in terms of elongation, the modulus equals one hundred times the quotient (stress/ strain.) The modulus is determined at 1 /2% elongation based on the slope of the curve at l /2%. The modulus is obtained from yarn stress-strain curves measured by the Instron tensile tester, which stretches the yarn at a constant rate of elongation. From the stress-strain curve, the stress is measured graphically at 1 /2% elongation on the initial linear portion of the stress-strain curve; and the modulus is calculated at one hundred times this value, divided by the denier of the filament sample.

From the above it is seen that the process afiords numerous advantages, the most important of which is that yarn having significantly reduced shrinkage and reduced tendency to retract can be produced without sacrifice ofi other physical properties. The method can be practiced with only slight modification of commercially employed apparatus. In addition, the rate at which the yarn can be processed is completely acceptable. Any additional 7 cost of using the method is far outweighed by the improvement in the properties of the yarn. Other advantages may be noted.

Any departure from the description herein that conforms to the spirit of the invention is intended to be included Within the scope of the claims.

What is claimed is:

1. A process for treating nylon filaments comprising the steps of longitudinally feeding nylon filaments capable of being molecul'arly oriented to a first stretch zone at a predeterminined rate, withdrawing the said filaments from said first zone at a predetermined increased rate, whereby the filaments are attenuated therein, snuobing the movement of said filaments through the said first zone so that there is a tendency of the point of the necking down of the filaments to be localized, passing the said filaments through a second stretch zone and withdrawing same therefrom at a predetermined increased nate, whereby the filaments are stretched a second time, snulbbing the movement of said filaments though the said second zone and heating the filaments at the same time, the overall draw ratio employed being about 2.5-5.5 and the draw natio employed in the second stretch zone being about 1.21.9, heating the yarn under low tension permitting the yarn to shrink about 6-10 percent, and taking the filaments up in an orderly manner.

2. The proces of claim 1 in which the filaments in the second zone are heated to a temperature of about 130- 220 C.

3. The process of claim 2 in which the temperature of the filaments when snubbed in the first zone is about 20-85 C.

4. A process for treating nylon filaments comprising the steps of continuously longitudinally feeding freshly spun nylon filaments capable of being molecularly oriented to a first stretch zone at a predetermined rate, continuously Withdrawing the said filaments from said first zone at a predetermined increased rate, whereby the filaments are stretched therein to increase the orientation thereof, continuously snubbing the movement of said filaments through the said first stretch zone so that there is a tendency of the point of necking down of the filaments to be localized, the temperature of the filaments when snubbed in the first zone being 20-85 C., passing the said filaments through a second stretch zone and Withdrawing same therefrom at a predetermined increased rate, whereby the filaments are stretched a second time, snubbing the movement of said filaments through the said second zone and heating the said filaments at a temperature about 130220 C. at the same time, the overall draw ratio employed being 2.55.5 and the draw ratio employed in the second stretch zone being about 1.'41.7, heating the yarn at a temperature of about 130-220 C. under low tension permitting the yarn to shrink about 6-10 percent, :and taking the filaments up in an orderly manner.

References Cited in the file of this patent UNITED STATES PATENTS 2,289,232 Babcock July 7, 1942 2,584,779 Avems et a1. Feb. 5, 1952 2,956,330 Pitzl Oct. 18, 1960 

1. A PROCESS FOR TREATING NYLON FILAMENTS COMPRISING THE STEPS OF LONGITUDINALLY FEEDING NYLON FILAMENTS CAPABLE OF BEING MOLECULARLY ORIENTED TO A FIRST STRETCH ZONE AT A PREDETERMINED RATE, WITHDRAWING THE SAID FILAMENTS FROM SAID FIRST ZONE AT A PREDETERMINED INCREASED RATE, WHEREBY THE FILAMENTS ARE ATTENUATED THEREIN, SNUBBING THE MOVEMENT OF SAID FILAMENTS THROUGH THE SAID FIRST ZONE SO THAT THERE IS A TENDENCY OF THE POINT OF THE NECKING DOWN OF THE FILAMENTS TO BE LOCALIZED, PASSING THE SAID FILAMENTS THROUGH A SECOND STRETCH ZONE AND WITHDRAWING SAME THEREFROM AT A PREDETERMINED INCREASED RATE, WHEREBY THE FILAMENTS ARE STRETCHED A SECOND TIME, SNUBBING THE MOVEMENT OF SAID FILAMENTS THROUGH THE SAID SECOND ZONE AND HEATING THE FILAMENTS AT THE SAME TIME, THE OVERALL DRAW RATIO EMPLOYED BEING ABOUT 2.5-5.5 AND THE DRAW RATIO EMPLOYED IN THE SECOND STRETCH ZONE BEING ABOUT 1.2-1.9, HEATING THE YARN UNDER LOW TENSION PERMITTING THE YARN TO SHRINK ABOUT 6-10 PERCENT, AND TAKING THE FILAMENTS UP IN AN ORDERLY MANNER. 